I'm sure that everyone has seen one example or another of people tweaking out when they're on various psychoactive drugs, but what's going on at a cellular level during these episodes?
It may be tough to fathom, but the "enriched" experience that many drugs offer tends to have a very specific origin somewhere in the brain. Whether it be in disrupting particular synaptic connections, changing the levels of circulating chemicals in your neural systems, or releasing neurotransmitters that have a wide range of effects, you can always tie a particular psychological phenomenon to neural activity.
So, what might this activity look like? Well, here's an interesting little applet that allows you to explore the cellular effects of various mind-altering drugs. It doesn't go into a huge amount of detail beyond the systems level, but pretty interesting nonetheless. (note, no mice were harmed in the making of this application)